As a heat storage device, one disclosed in Patent Literature 1 has been known, for example. The heat storage device disclosed in Patent Literature 1 comprises a reaction vessel for containing a heat storage member which reversibly causes exothermic and endothermic reactions with a reaction medium, a storage vessel for storing the reaction medium, a communication passage for communicating the reaction and storage vessels to each other, so as to enable the reaction medium to circulate between the reaction and storage vessels, and a heater for heating the reaction medium in the storage vessel.